This application is based on Japanese Patent Application No. 2001-69206 filed on Mar. 12, 2001 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an apparatus for controlling an engine, which is capable of switching the fuel combustion mode among the lean-fuel, stoichiometric, and rich-fuel combustion.
2. Description of Related Art
There have been proposed internal combustion engines which are controlled to have air-fuel ratios leaner than the stoichiometric ratio. These internal combustion engines have their fuel combustion mode controlled to switch among lean-fuel combustion, stoichiometric combustion and rich-fuel combustion depending on the operational state including the load condition.
Internal combustion engines vary the output torque abruptly at the switching of combustion mode due to the variation of air-fuel ratio or ignition timing, producing a large torque shock.
In this respect, a technique for alleviating the torque shock at the switching of combustion mode is described in JP-A No. H04-036042. The technique described in this patent publication is designed to vary the air-fuel ratio and ignition timing gradually at the switching of combustion mode, thereby alleviating the torque shock. Another technique described in JP-A No. H06-108824 is designed to control the retardation of ignition timing at the switching from lean-fuel combustion to rich-fuel combustion, thereby alleviating the torque shock.
Internal combustion engines which are controlled to perform lean-fuel combustion are intended to achieve the better fuel efficiency, and it is demanded to improve the fuel efficiency to the largest extent on condition that the toxic emission and drivability are not aggravated.
However, the technique described in JP-A No. H04-036042 causes the transitional time of combustion mode to extend, and a resulting longer duration of passage across the air-fuel ratio zone of the worst NOx emission will produce an increased amount of NOx.
The technique described in JP-A No. H06-108824 is based solely on the ignition retardation for the reduction of torque increase at the switching from lean-fuel combustion to rich-fuel combustion, and the need of a large ignition retardation will aggravate the state of combustion. The aggravate combustion involved in this technique will result in a degraded fuel efficiency.
In view of the foregoing prior art deficiencies, it is an object of the present invention to provide an apparatus for controlling an engine, which is capable of reducing the torque shock at the switching between rich-fuel combustion and stoichiometric or rich-fuel combustion, and also preventing the fall of fuel efficiency.
According to the present invention, a controller computes the response of intake air quantity based on the variation of opening of the throttle valve in the transition of combustion mode, and modifies the fuel injection quantity and ignition timing based on the intake air response.
When the combustion mode is switched, the intake air quantity, fuel injection quantity and ignition timing are changed to accord with the post-switching combustion mode. The time expended until the control value shifts to that for the post-switching combustion mode differs among the intake air quantity, fuel injection quantity and ignition timing. Among these control values, the intake air quantity is the slowest to reach the post-switching control value, and the controller implements a step-wise change of throttle valve opening to the post-switching opening value, thereby performing the quick switching of combustion mode. The controller modifies the fuel injection quantity and ignition timing based on the intake air response evaluated in the transition of combustion mode.
By reducing the torque shock without relying on a drastic ignition retardation control, the aggravation of combustion can be prevented. By changing the throttle valve opening in step-wise fashion to the post-switching opening value, it is possible to vary quickly the intake air quantity which is slower in response as compared with the ignition timing and fuel injection quantity. A resulting quick transition of combustion mode decreases the duration of passage across the air-fuel ratio zone of the worst NOx emission, and thus can reduce the toxic emission.
Furthermore, the modification of ignition timing and fuel injection quantity based on the intake air response evaluated in the transition of combustion mode does not necessitate drastic ignition retardation for the reduction of torque shock, and thus the aggravation of combustion can be prevented.
The response of intake air quantity may alternatively be computed based on the intake air quantities before and after the switching of combustion mode and the inferred immediate intake air quantity, in which case the fuel injection quantity and ignition timing can be modified more accurately.
The fuel injection quantity may be modified based on the variation of fuel injection quantities and intake air quantities before and after the switching of combustion mode. The ignition timing may be modified based on the variation of ignition timings and intake air quantities before and after the switching of combustion mode. In these cases, the fuel injection quantity or ignition timing can be set accurately at the switching of combustion mode.
The fuel injection quantity and ignition timing may be modified based on the response of exhaust gas recirculation (EGR) quantity.
Exhaust gas recirculation control mean is designed to set the control values depending on the combustion mode in the same manner as the intake air quantity, fuel injection quantity and ignition timing. When the exhaust gas recirculation control means introduces exhaust gas and intake air into the engine, fuel combustion is disturbed. Specifically, the fuel combustion is liable to be unstable at lean-fuel combustion, and the quantity of exhaust gas recirculation relative to the intake air quantity is reduced during the combustion at air-fuel ratios leaner than the stoichiometric ratio so as to prevent the disturbance of combustion.
When the combustion mode is switched, the proportion of exhaust gas recirculation relative to intake air can possibly increase due to the difference of response between the exhaust gas recirculation quantity and the intake air quantity during the mode transition, resulting possibly the arising of a torque shock. In this case, by modifying the fuel injection quantity and ignition timing based on the responses of exhaust gas recirculation quantity and intake air quantity, the torque shock can be reduced and the accurate combustion mode switching control can be performed.
At the switching of combustion mode, the target value of the exhaust gas recirculation quantity may be switched in step-wise fashion to the post-switching target value. Based on the step-wise switching of the exhaust gas recirculation quantity in addition to the intake air quantity, the mode transition takes place quickly, allowing the quick passage across the air-fuel ratio zone of the worst NOx emission during the transition, for example, from rich-fuel combustion to lean-fuel combustion, and vice versa, and consequently the toxic emission can be reduced.
Alternatively, the fuel injection quantity and ignition timing may be modified based on one of the fuel injection response and exhaust gas recirculation response so that the output torque increases during the transition of combustion mode, and in addition the amount of ignition timing retardation may be set based on the difference between the intake air response and the exhaust gas recirculation response. In consequence, the torque shock arising at the switching of combustion mode can be alleviated.
By modifying the base fuel injection quantity and base ignition timing, the fuel injection quantity and ignition timing may be set in accordance with one of the fuel injection response and ignition timing response during the mode transition.
The quantity of exhaust gas recirculation into the engine can be controlled based on either a variable valve timing device or an exhaust gas recirculation valve.
By modifying the fuel injection quantity and ignition timing based on whichever response that is faster among the intake air and exhaust gas recirculation, it is possible to control the engine always to the torque increase side at the switching of combustion mode. The ignition timing which has been modified based on the faster response may be rendered the modification of retardation based on the intake air response and exhaust gas recirculation response. In consequence, the switching of combustion mode can take place faster, and the torque shock at the transition can be alleviated.
By modifying the fuel injection quantity and ignition timing based on whichever response that is slower among the intake air and exhaust gas recirculation, it is possible to control the engine always to the torque increase side at the switching of combustion mode. The ignition timing which has been modified based on the slower response may be rendered the modification of retardation based on the intake air response and exhaust gas recirculation response. In consequence, the switching of combustion mode can take place faster, and the torque shock at the transition can be alleviated.
By modifying the fuel injection quantity and ignition timing based on whichever response that causes a torque increase among the exhaust gas recirculation and intake air, it is possible to control the engine always to the torque increase side at the switching of combustion mode. The modified ignition timing may be rendered the modification of retardation based on the difference of the exhaust gas recirculation response and the intake air response. In consequence, the torque shock at the transition of combustion mode can be alleviated.
At a mode switching from lean-fuel combustion to stoichiometric or rich-fuel combustion, the computation of fuel injection quantity and ignition timing may be implemented based on the exhaust gas recirculation response. In consequence, the torque shock caused by the difference of response between the exhaust gas recirculation and the intake air can be brought to the increase side. By the rendition of the modification of the ignition retardation to the modified ignition timing based on the difference of response between the exhaust gas recirculation and the intake air, it is possible to alleviate significantly the torque shock arising at the switching of combustion mode.
Similarly, at a mode switching from rich-fuel or stoichiometric combustion to lean-fuel combustion, the modification of the fuel injection quantity and ignition timing may be implemented based on the intake air response. In consequence, the torque shock caused by the difference of between the exhaust gas recirculation response and the intake air response can be brought to the increase side. By the rendition of the modification of ignition retardation to the modified ignition timing based on the difference of response between the exhaust gas recirculation and the intake air, it is possible to reduce significantly the torque shock arising at the switching of combustion mode.